Plastic lenses are used for mobile phones, digital cameras, vehicle-mounted cameras, and the like, and are required to have excellent optical characteristics suitable for the purpose of the device. Plastic lenses are also required to have high durability including, for example, heat resistance and weather resistance, and high productivity that allows them to be molded at good yield, according to the form of use. Transparent resins such as polycarbonate resins, cycloolefin polymers, and methacrylic resins, for example, have been used as resin materials for the plastic lens.
In recent years, in order to achieve a reduction in mounting costs, methods for mounting camera modules collectively by solder reflow have been proposed, and plastic lens materials for use in these methods have been demanded to be able to withstand a high-temperature thermal history (for example, 260° C.) in the solder reflow process. However, conventional plastic lenses, which are produced by injection-molding thermoplastic resins, have low heat resistance, and are difficult to adapt to the reflow process satisfactorily. Thus, the molding process for molding lenses for reflow mounting is shifting toward press molding that uses curable resins liquid at room temperature.
Meanwhile, a plurality of lenses are used for a high-resolution camera module, in which one of the lenses is required to be an optical material with a high refractive index and a low Abbe's number that serves as a wavelength correction lens. In particular, there has recently been an increasing demand for thinner camera modules, which has required a lens material having a high refractive index (for example, 1.62 or more) and a low Abbe's number (for example, 26 or less).
As disclosed in Patent Document 1, however, most of the conventional materials proposed as materials featuring high refractive index only have improved heat resistance to temperatures not higher than 200° C., and have failed to ensure heat resistance to withstand the solder reflow process at 260° C., for example.
Meanwhile, since satisfactory reflow heat resistance cannot be readily achieved by using organic materials alone, materials provided with heat resistance by mixing organic materials with inorganic particles such as silica have been proposed (see Patent Document 2, for example). In these materials, however, the silica content needs to be increased to achieve satisfactory heat resistance, which has the drawback of precluding an increase in the refractive index of the composition. Moreover, these materials are poor in reliability, because they may have decreased transparency due to the aggregation of the inorganic particles, or may result in brittleness in cured products due to the addition of the particles.